Process for treating washable leather



United States Patent 3,300,338 PROCESS F012 TREATING WASHABLE LEATHER Martin L. Fein, Philadelphia, Samuel J. Viola, Norristown, and Edward M. Filachione, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of Agriculture N0 Drawing. Filed Feb. 20, 1964, Ser. No. 346,355 12 Claims. (Cl. 117-142) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to and has among its objects the treating of washab'le leather so that the leather retains certain desira'ble characteristics through many wash cycles.

For the purpose of this application the term washable leather is defined as follows: the leather is able to be washed in hot soap (detergent) solutions in a specific, standardized test (A.S.T. M. designation D 2096-621- washing procedure only), remaining relatively unchanged physically and chemically when compared to an unwashed specimen of the same leather, and the shrinkage temperature (T of the washed leather must not drop drastically after each wash. The difference in Washability of leathers is demonstrated by theresults summarized in the table TABLE.EFFECT 0F WASHING ON SHRINK TEMPERA- TURE OF CHROME-TANNED AND CHROME-TA'N NED, GLUTARALDEHY'DE RETA NNED CABRETTA SKINS Shrink Temperatures (TB, C.)

Glutaraldehyde Retannage B efore Washing After Washing* 1st 2nd 3rd AT C.

*Washed in Launder-Ometer; each wash=% hr., 120 F., 0.5% soap solution.

The marked reduction in shrink temperature of the chrome-tanned skin shows that a typical chrome-tanned garment or glove leather is not washable according to our definition. The washable leather of the present invention is demonstrated with glutaraldehyde and glutaraldehydechrome tanned leathers.

After several washes, even washable leather :begins to lose its pleasing character. For garment leather especially it is necessary that the leather have good drape, and hand and well-nourished feel. There is very little information on the effect of washing on the fat liquor incorporated into leather. Our experimental work has shown that washing does not remove as much of the fat "liquors as might be expected considering their composition and the way they are put into the leather. However, washed leather tends to develop a harsh, dry feel.

A particular object of the present invention is to provide a process for preventing this harsh, dry feel in washed leather especially in garment leather washed by a home laundry procedure.

We have found that certain compounds can be used to treat the washable leather before, during, and after the wash cycle, and these compounds will help the leather retain its pleasing feel, drape and hand. The leather will continue to appear well nourished, soft and flexible after each wash, comparing favorably with an unwashed piece. The washing procedure (see ASTM designation mentioned above) use-d as a criterion in this 3,30053'3'8 Patented Jan. 24, 1967 application is much more drastic than that which would normally be indicated for home or commercial use. Even so, excellent results are obtained for at least eight wash cycles. Such agents are long chain amphoteric compounds, with anionic and cationic activity depending on the pH at which they are used. This differs from the softening-agents generally used in home or commercial laundering which are the straight cationic type. The cationics give relatively poor results on leather.

The above discussion applies also to washable tanned pelts from wool and fur bearing animals. In the case of shearli-ngs, for example, the appearance and feel of the sheared wool continues to compare favorably with unwashed pieces after numerous wash cycles. In addition, they dry more readily than washed pieces that are untreated.

According to the present invention the properties of softness, smoothness and other closel associated physical characteristics are imparted to washable leather by a process comprising impregnating said leather with an aqueous solution of a compound of the formula wherein R is a long carbon chain aliphatic radical, M is selected from the group consisting of hydrogen and a water-soluble salt forming cation, and Y is selected from the group consisting of hydrogen and wherein M is as previously recited, separating the impregnated leather from the solution and drying the leather.

In a preferred series of compounds R in the formula represents a fatty group derived from the acids present in natural fats and oils such as tallow and coconut oil, that is, long carbon chain, predominantly C -C aliphatic radicals.

Whereas, M is a water-soluble salt-forming cation this will often be sodium, many other cations fit this category, including potassium, ammonium, and substituted ammonium groups such as triethanolamine.

The rare amphoteric type compound employed in the process of the present invention has an isolelectric point at which it has minimum solubility in water. The aqueous solution used for impregnating the leather is, at least initially, necessarily at a pH above or below the isoelectric point.

At a pH either higher or lower than the isoelectric point a 1% aqueous solution in a volume of solution adequate for tumbling the leather was found to contain an excess of the compound over that necessary to provide the desired result.

In a preferred embodiment of the present invention the leather is impregnated with the aqueous solution of the compound, followed by an adjustment of the pH of the solution to a point at or near the isoelectric point. The leather is then dried at room temperature. When dry the leather is ready for use with very little working or shaping. Such physical manipulation as hand working or staking is required in the processing of all garment and glove leathers when they are dried from wet processing steps in leather making. The adjustment of pH :assures adequate retention of the compound in and on the leather, achieving full softening and also surface smoothness in case of grain leathers. The desirable effects of the compound are quite durable and so it need not be used every time the leather is washed.

' While it is considered that the application is most efliciently conducted as an after-rinse or treatment after the leather has been washed, the process of the present invention may be otherwise employed. Because these agents are surfactants, in addition to being amphoteric, the process can be performed as a washing operation, with the compound alone or in combination with soap or detergent.

Moreover, we have found these compounds can be used alone as a complete lubricating agent, instead of fatliquors, or they can be used in combination with the standard types of fat-liquors normally used in these leathers.

These compounds can be used, also, to replace the detergent components of the normal fiat-liquor mixture such as sulfated oil emulsifying agents. Thus, the deterioration of the leather due to the formation of acids (such as sulfuric acid from sulfonated oils) can be avoided.

In use as a fat-liquoring agent the concentration of compound in solution may be varied over a wide range, but, depending upon the type of leather being processed, concentrations which provide from 2 to by weight of the wet drained tanned skin are preferred.

In contrast to emulsion-type fat liquors wherein the oil may be exhausted from the emulsion, the solution type fat liquors of the present process are not readily exhausted even when driven out of solution at the isoelectric point. Upon removal of the treated leather, the solution can be reused. If the solution is at a pH near the isoelectric point the pH is adjusted so that insoluble agent is redissolved. If necessary the concentration of the compound in the fatliquor medium is increased by dissolving additional compound.

In order that those skilled in the art may better understand how the present invention can be carried into effect, the following examples are given by way of illustration and not by way of limitation.

Example 1 Eight specimens of glutaraldehyde tanned leather, each 2 x 3 /2 inches, cut from the same leather sample were washed according to the procedure outline in American Society for Testing Materials (A.S.T.M.) designation D2096-62T (washing procedure only). The quantity of soap solution used was adjusted for the greater number of samples needed to carry out the eight wash cycles as compared to the three cycles required by the A.S.T.M. test listed above. The leather specimen removed after each wash cycle was rinsed essentially free of soap in running water. The specimen was then tumbled for about 10 minutes in 50 cc, of 1% solution of a mixture of N- lauryl-B-amino propionic acid and N-myristyl- -amino pr-opionic acid, in water (pH 6 to 7.5) at the same temperature as during the wash period. Glacial acetic acid was added dropwise to the solution to pH 3 and the tumbling continued for an additional minutes. At the end of this period the leather specimen was removed from the jar, and spread on a towel to air-dry.

The remaining seven specimens were washed again according to the specified procedure. The second specimen was removed and treated as described above. This was repeated until all the specimens were removed, one by one, from the repeating wash cycles and each treated with the N-lauryl-myristyl-{i-amino propionic acid.

All eight specimens, when dry, compared favorably with an unwashed piece; they were soft, flexible and essentially unchanged in size and shape after very little hand workmg.

Example 2 The procedure was performed as described in Example 1 except that the leather specimens were cut from a sample tanned with chrome tanning agent and retanned with glutaraldehyde. All washed and treated samples, when dry, were as described in Example 1.

Example 3 The procedure followed was that described in Example 1 except that the final treatment reagent was a mixture of N-alkyl-fl-amino propionic acids in which the alkyl groups are derived from coconut oil fatty acids and the adjustment in acidity was to pH 4.5. The washed and treated specimens were, when dry, soft and flexible like those described in Example 1.

Example 4 The procedures of Example 3 were applied to leather specimens from a skin tanned with chrome tanning agent and retanned with glutaraldehyde. The results were similar to that of Example 1.

Example 5 Example 1 was repeated with the exception that the compound in the aqueous solution was the partial sodium salt of N-lauryl-B iminodipropionic acid,

C H N CH CH COOH) CH CH COONa Results were excellent, the final dry specimens being soft and flexible regardless of the number of washes.

Example 6 This example was similar to Example 5 except that the leather specimens were from a sample tanned with chrome tanning agent and retanned with glutaraldehyde.

All the treated specimens were soft, flexible and essentially unchanged in size and shape from an unwashed specimen of the same leather.

The foregoing examples demonstrate the application of the compounds to the leather in a process following a wash cycle.

It is to be understood that in the preferred process in which the pH of the aqueous phase is adjusted to the isoelectric point, that the pH desired will vary depending upon the compound or mixture of compounds employed. The adjustments exemplified, to pH 3.0 and 4.5, are appropriate for the compounds employed in the particular examples, but are not intended to be in limitation of the process.

' Examples 7 to 9 describe the process in which the washable leather has just been tanned and the process alone, or'

in combination with typical fat liquoring agents, is employed as a finishing process.

Typical fat liquoring agents are animal and vegetable oils such as cod, neatsfoot, coconut and tall oils, often blended for application, and with sulfonated derivatives added to stabilize the aqueous emulsion.

Example 7 A wet piece of glutaraldehyde tanned cabretta skin (drained weight=33 grams) was placed in a jar containing 6.6 grams of a 45% aqueous solution of N-coco-B- amino propionic acid (coco=alkyl groups derived from coconut oil fatty acids), in ml. of water. The jar was placed on a tumbling apparatus and run for /2 hour. Concentrated acetic acid was added dropwise tothe cloudpoint (isoelectnic point) and then the jar was replaced on the tumbling apparatus for about two hours. Finally the skin was removed and spread out to dry. The leather, when dry and with very little working, was smooth, soft and had an excellent appearance and feel. The strength was excellent. A specimen of the leather was washed seven times according to the A.S.T.M. washing procedure previously noted in this application. Examination of the dry leather after each of the first four washes showed the leather compared favorably with an unwashed piece. Some surface dryness was detected after the fifth wash. After the sixth wash the specimen was tumbled for 10 minutes in a jar containing 50 cc. of a 1% solution of N-coco-B-amino propionic acid in water. Glacial acetic acid (0.15 ml.) was added to the solution (to the isoelectric point) and the jar was replaced on the tumbler for 20 minutes. At the end of this period the leather was removed and spread out to dry. The air dried leather, with very little working, had lost the surface dryness and w s again excellent in feel and appearance as well as in strength. The specimen was washed once more without the after-rinse treatment and desired properties were still evident; the leather was essentially the same as before the seven wash cycles.

Example 8 A wet piece of glutaraldehyde tanned cabretta skin (drained weight=29 grams) was placed in a jar containing 1.5 grams sulfated neatsfoot oil and a mixture of 3.0 grams N-lauryl-fl-amino propionic acid and N-myristyl- /3-amino propionic acid in 100 ml. of water. The jar was placed on a tumbling apparatus and run for about one hour. A heat lamp was directed on the jar for about /2 hour of this period. Several drops of concentrated acetic acid were added to the solution to the cloud-point (isoelectric point) and the jar was returned to the tumbling apparatus for another hour. The skin was then removed from the jar and spread out to dry. The leather when dry was excellent.

Example 9 A wet piece of glutaraldehyde tanned cabretta skin (drained weight=28 grams) was placed in a jar containing 2.0 grams neatsfoot oil (cold pressed) and a mixture of 2.0 grams N-lauryl-B-amino propionic acid and N- myristyl-fl-amino propionic acid in 100 ml. of water. The jar was placed on a tumbling apparatus and run for about two hours. A heat lamp was directed on the jar during this period. Five drops of concentrated acetic acid were added to the solution-emulsion which then changed toa clear liquid phase with some solid particles suspended. The jar was replaced into the tumbling apparatus for about two hours. The skin was then removed from the jar and spread out to dry. The leather, when dry, was excellent in strength, appearance and feel.

We claim:

1. A process for imparting softness and smoothness to washable leather comprising impregnating said leather with an aqueous solution of a compound of the formula and mixtures thereof, wherein R is a long chain aliphatic radical having from 11 to 17 carbon atoms inclusive, M is selected from the group consisting of hydrogen and a water-soluble salt-forming cation, and Y is selected from the group consisting of hydrogen and CH CH COOM wherein M is as previously recited, separating the impregnated leather from the solution and drying the leather.

2. The process of claim 1 in which the leather impregnated with the aqueous solution is washed, washable leather.

3. The process of claim 1 in which the leather impregnated with the aqueous solution is non-fat-liquored, tanned, washable leather.

4. A process for imparting softness and smoothness to washable leather comprising impregnating said leather with an aqueous solution of a compound of the formula and mixtures thereof, wherein R is a long chain aliphatic radical having from 11 to 17 carbon atoms inclusive, M is selected from the group consisting of hydrogen and a water-soluble salt-forming cation, and Y is selected from 6 the group consisting of hydrogen and CH CH COOM wherein M is as previously recited, adjusting the pH of the aqueous solution to about the isoelectric point of said compound, separating the impregnated leather from the solution of adjusted pH and drying the leather.

5. The process of claim 4 in which the leather impregnated with the aqueous solution is washed, washable leather.

6. The process of claim 5 in which, in the formula, R consists of radicals derived from the fatty acids of coconut oil, Y is hydrogen and M is hydrogen.

7. The process of claim 5 in which the mixture of compounds consists essentially of N-lauryl- B-amino propionic acid and N-myristyl-B-amino propionic acid.

8. The process of claim 5 in the compound is the monosodium salt of N-lauryl-fl-iminodipropionic acid.

9. The process of claim 4 in which the leather impregnated with the aqueous solution is non-fat-liquored, tanned, washable leather.

10. The process of claim 9 in which, in the formula, R consists of radicals derived from the fatty acids of coconut oil, Y is hydrogen and M is hydrogen.

11. A process for imparting softness and smoothness to washable leather comprising impregnating freshly tanned leather with an aqueous medium containing a fat liquoring agent and a compound of the formula and mixtures thereof, wherein R is a long chain aliphatic radical having from 11 to 17 carbon atoms inclusive, M is selected from the group consisting of hydrogen and a water-soluble, salt-forming cation, and Y is selected from the group consisting of hydrogen and CH CH COOM wherein M is as previously recited, separating the impregnated leather from the solution and drying the leather.

12. A process for imparting softness and smoothness t0 washable leather comprising impregnating freshly tanned leather with an aqueous medium containing a fat liquoring agent and a compound of the formula and mixtures thereof, wherein R is a long chain aliphatic radical having from 11 to 17 carbon atoms inclusive, M is selected from the group consisting of hydrogen and a water-soluble, salt-forming cation, and Y is selected from the group consisting of hydrogen and CH CH COOM wherein M is as previously recited, adjusting the pH of the aqueous medium to about the isoelectric point of said compound, separating the impregnated leather from the solution of adjusted pH, and drying the leather.

References Cited by the Examiner UNITED STATES PATENTS 2,468,012 4/1949 Isbell 260534 2,810,752 10/1957 Freese 260-534 2,814,643 12/ 1957 Aelony 260534 2,816,920 12/1957 Anderson 260534 2,974,000 3/1961 Retzsch et a1 8-94.23

WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner. 

1. A PROCESS FOR IMPARTING SOFTNESS AND SMOOTHNESS TO WASHABLE LEATHER COMPRISING IMPREGNATING SAID LEATHER WITH AN AQUEOUS SOLUTION OF A COMPOUND OF THE FORMULA 